code: def test_ObservationDataValidation(self) -> None:
      with self.assertRaises(ValueError):
          ObservationData(
              metric_names=["a", "b"],
              means=np.array([4.0]),
              covariance=np.array([[1.0, 4.0], [3.0, 6.0]]),
          )
      with self.assertRaises(ValueError):
          ObservationData(
              metric_names=["a", "b"],
              means=np.array([4.0, 5.0]),
              covariance=np.array([1.0, 4.0]),
          )
  
imports: import json
  from unittest.mock import Mock, PropertyMock
  import numpy
  import pandas
  from ax.core.arm import Arm
  from ax.core.base_trial import TrialStatus
  from ax.core.batch_trial import BatchTrial
  from ax.core.data import Data
  from ax.core.generator_run import GeneratorRun
  from ax.core.map_data import MapData, MapKeyInfo
  from ax.core.observation import Observation, ObservationData, ObservationFeatures, observations_from_data, observations_from_map_data, recombine_observations, separate_observations
  from ax.core.trial import Trial
  from ax.utils.common.testutils import TestCase
label_desc: Use image node_id 6 for calling the ObservationsTest obj's underlying member method code with example usage: obj.test_ObservationDataValidation() without return types